Kautilya's Arthashastra 7.5.11

7.5.11

tasmād viraktaprakṛtim eva yāyāt //

When the enemy of virtuous character and under worse troubles is attacked, his subjects will help him; whereas, the subjects of the other of vicious character and under less troubles will be indifferent. Disloyal or indifferent subjects will endeavour to destroy even a strong king. Hence the conqueror should march against that enemy whose subjects are disloyal.